The subject matter disclosed herein relates to process monitoring systems and, more particularly, to a number of pluggable bases which may be connected together in a monitoring system configuration and where the bases may comprise different levels of redundancy.
In the process industry, various processes and assets inherently have differing levels of criticality. Criticality may typically be determined by the damage resulting from failure of that asset in terms of environmental, health and safety, lost production, and the cost of replacement or repair of the asset itself. Likewise, certain measurements made using sensors applied to the assets may carry different levels of criticality. In this case, criticality is determined by the amount of time the control system or operator has to respond to the problem and whether there are other indicators of the problem. For example, the response to a thrust position failure in a gas turbine engine may require a much more rapid response time than an elevated casing vibration.
A single monitoring or control system may be applied to multiple assets of differing criticality each of which may have measurements of different criticality. The criticality of the assets and measurements drive the necessary reliability of the monitoring or control equipment. Higher reliability is typically achieved using redundancy. There are many levels of redundancy with regard to sensing, processing, etc. that may be used to achieve specific levels of reliability. For example, fully triple-modular-redundant (TMR) systems with redundant sensors may be used to provide relatively high levels of reliability. For another measurement, a single sensor may be bussed to, for example, three redundant processing modules. While this configuration does not offer as high a level of reliability as the full TMR system, the bussed sensor redundant system does exhibit significantly higher reliability than a simplex or dual redundant system because the processing module, which has the highest complexity and thus the highest probability of failure, has been made redundant.
In addition to the various sensor measurements, there may be other signals shared between the various modules of the system. These signals will include power (may be redundant), communication networks (may be redundant), machine speed timing signals, and module asset information signals. The cost of running discrete wires or cables negatively impacts the system cost due to the costs of wire termination, wire identification, and the design documentation. Also, discrete wires and connectors have a higher probability of failure than do internal electronic assembly traces and thus can cause a decrease in reliability.
There are currently several different solutions for mixed levels of redundancy, none of which are relatively well suited for the criticality issues involved. In one solution, a TMR capable system backplane structure along with a TMR capable interface module is provided. Redundant and simplex modules may be intermixed within the system, however, all modules share the expense of the redundant capable backplane and interface module infrastructure. If it is desired to bus the same sensor signal across multiple modules, external wires or an external break out board is typically used. This results in a large number of external wires. In another solution, redundant sets of individual modules each with its own sensor or bussed sensors are deployed individually, the output from each is sent to a voting module which provides the final output based on a predefined voting (such as 2 out of 3) of the signals. In yet another solution, a number of TMR processor modules provide redundant processing power for all measurements. Input and output modules may be added to the system with varying levels of redundancy, however, since the processing modules must be capable of processing all I/O signals, the TMR system carries the added cost of three high-power redundant processing modules regardless of whether all measurements need to be processed redundantly. These known systems typically reserve space for redundant I/O modules resulting in relatively large footprint space requirements.